1. Field of the Invention
The present invention relates to a method for estimating an optimized transmission bit rate in a wireless local area network (LAN) system, and more particularly, to a method for estimating an optimized transmission bit rate in a wireless LAN system, which is to provide an accurate data transmission bit rate according to channel status when block data are transmitted in the wireless LAN system.
2. Description of the Related Art
The physical layer of a wireless LAN system to which IEEE 802.11 is applied supports a variety of transmission bit rates using different modulation and coding schemes. For example, IEEE 802.11a supports eight transmission bit rates between 6 Mbps to 54 Mbps, IEEE 802.11b supports four transmission bit rates between 1 Mbps to 11 Mbps, and IEEE 802.11g supports twelve transmission bit rates between 1 Mbps to 54 Mbps. Here, since each of the transmission bit rates has individual bit error characteristics, there usually exists a single optimized transmission bit rate in a given channel condition, and a lower transmission bit rate generally has further low bit error characteristics.
Accordingly, mobile communication network operators are encouraged to contrive a method for increasing a throughput by applying an optimized transmission bit rate, in which channel status changed in real-time according to time and space is reflected, to a mobile communication terminal and a mobile communication system.
In order to solve the problem, a method for estimating a transmission bit rate considering channel status has been applied to a mobile communication terminal. However, since the channel status is inaccurately measured when estimating a transmission bit rate or the channel status is rapidly changed, the mobile communication terminal frequently select a non-optimized transmission bit rate.
If it is attempted to transmit data at a transmission bit rate higher than an optimized transmission bit rate, the probability for the data transmission to fail is high. Contrarily, if it is attempted to transmit data at a transmission bit rate lower than the optimized transmission bit rate, the success rate of the data transmission is increased. However, there is a problem in that transmission efficiency is decreased since the channel is unnecessarily occupied for an extended period of time.
The side-effect of selecting an inappropriate transmission bit rate gets severer when the block acknowledgement (BA) scheme defined in the IEEE 802.11e is applied.
In more detail, if a plurality of data frames (MAC protocol data unit: MPDU), which are grouped as a block, are consecutively transmitted, only one block acknowledgement is transmitted in response thereto. Therefore, waste of bandwidth can be reduced as compared with transmitting an acknowledgement for each data frame. However, since a plurality of data frames are transmitted at a time before transmitting an acknowledgement, the same transmission bit rate is applied to each of corresponding data frames that are grouped as a block.
Accordingly, when transmitting data using the block acknowledgement scheme, inappropriate increase of a transmission bit rate invites transmission failure of a plurality of frames, and inappropriate decrease of a transmission bit rate invites waste of channel bandwidth for an extended period of time compared with transmitting a single frame.